Undefined reference to static vector

[Deanus94]

Hi all! First post here :)

I'm trying to create a class that creates and stores objects of type T in a static vector, and returns a reference to that object so I can use it in main(), as shown in the code below:


internvect.h:

template<class T>
class InternVect
 {
   protected:
   
   	InternVect() { }
   	
   	static std::vector<T> vAll;
   	
   public:
   
  	static T& create() {
		vAll.push_back(T());
		return vAll.back();
	  }
 };

main_tman.cpp:

#include "internvect.h"
int main ()
 {
	int &i = InternVect<int>::create();
	
	std::cout<<i<<std::endl;
	
 	return 0;
 }

I am getting the following error:

g++-10 -I inc -I ../../inc src/main_tman.cpp -o bin/out
/usr/bin/ld: /tmp/ccoOzb7F.o: in function `InternVect<int>::create()':
main_tman.cpp:(.text._ZN10InternVectIiE6createEv[_ZN10InternVectIiE6createEv]+0x2c): undefined reference to `InternVect<int>::vAll'
/usr/bin/ld: main_tman.cpp:(.text._ZN10InternVectIiE6createEv[_ZN10InternVectIiE6createEv]+0x38): undefined reference to `InternVect<int>::vAll'
collect2: error: ld returned 1 exit status
make: *** [Makefile:15: compile] Error 1

Can anyone tell me what am I missing, or a better way to do it?

Thanks!
Dean

[dutch]

You need an implementation file to actually instantiate the vector:

// internvect.cpp

#include "internvect.h"

template<class T> std::vector<T> InternVect<T>::vAll;

EDIT: You may be able to put that statement in the header file after the class definition, although I'm not entirely sure about that.

[Deanus94]

Thanks for your help! It actually worked only when placed at the end of the header file, not with a source file.

Dean